The Curious Case of the Antidepressant, Anti-anxiety Backyard Garden

Dr. Daphne Miller

YES! Photo by Kristin Little

Gardening is my Prozac. The time I dedicate to training tomato vines or hacking at berry bushes seems to help me stave off feelings of sadness or dread and calm the chatter in my mind. My vegetable beds have even buoyed me through more acute stressors, such as my medical internship, my daughter’s departure for college, and a loved one’s cancer treatment. I’m not alone in appreciating the antidepressant and anti-anxiety effects of gardening — countless blogs are dedicated to this very subject, and a rash of new studies has documented that spending time around greenery can lead to improved mental health.

Daphne Miller is a practicing family physician, associate professor at the University of California, San Francisco, senior adviser at the Prevention
Institute, and author of Farmacology and The Jungle Effect

“How does this work?” I asked Jill Litt several years ago when I first became interested in what I call gardening’s “bio-euphoric” effect and was wondering whether to prescribe this activity to my depressed patients. Litt, a professor at the University of Colorado School of Public Health, was studying gardening’s impact on a variety of health outcomes — including mood disorders. She rattled off a list of possible explanations, including that gardens create community, encourage physical activity, offer a bounty of nutrient-rich food, and expose one to Vitamin D-producing sunshine, which helps regulate serotonin, the “happiness” neurotransmitter. But then Litt surprised me by adding, “Also there are the microbes themselves. We have no idea what they are doing.”

The idea that microbes in our environment might impact our health was not new to me. It’s well-established that the microbes in soil enhance the nutritional value of food and, as found in studies of farm children in Bavaria and among the Indiana Amish, improve immune function. (Researchers were finding that exposure to a diversity of microbes early in life led to fewer allergies.) But garden microbes acting as mood enhancers — well, this was news to me.

I soon discovered that there is, in fact, evidence to back up this idea. It’s a smattering of data, and most of it has been collected on our distant cousins, the mice, but it is still compelling.

This investigation into the soil-mood connection began, like much of science, quite serendipitously. British researchers were testing whether immune stimulation with Mycobacterium vaccae, a harmless microbe found in soil and water and potentially on unwashed vegetables, might help treat lung cancer in humans. While they discovered unchanged life expectancy in the subjects treated with the M. vaccae, they were surprised that these patients scored much higher on a standard quality-of-life questionnaire than the controls. Somehow the bug had enhanced their mood.

This finding inspired another researcher, Chris Lowry, a behavioral endocrinologist at the University of Colorado Boulder, to inject heat-killed M. vaccae into the bronchi of mice. The rodents, like the cancer patients, seemed to derive a psychological benefit from the treatment, exhibiting less depression and anxiety on a stressful “forced swim test.” In their article in Neuroscience, Lowry and his colleagues hypothesize that the immune reaction to M. vaccae activates the release of brain serotonin leading to reduced stress-related behavior.

Building on Lowry’s work, Susan Jenks and Dorothy Matthews, two researchers at Sage Colleges in Troy, New York, decided to administer M. vaccae to their mice and perform a new set of behavioral tests. Instead of using the heat-killed M. vaccae used in previous experiments, they cultured the live organism and fed it to the mice via a concoction of Wonderbread and peanut butter. It occurred to me that this exposure method most closely mirrored how I might come in contact with M. vaccae: by eating the casually washed greens that I regularly harvest from my backyard.

YES! Photo by Kristin Little

“It was just amazing,” Jenks said, discussing a maze test designed to expose rodents to stressful new situations. “We would place them in the maze and could clearly see that there were some mice doing better than others. We would think: ‘Is that the M. vaccae [mouse]?’ And sure enough it was.”

Forever in search of safe, low-tech solutions that I can offer my patients, I asked Jenks whether her experiment was essentially suggesting that M. vaccae exposure by eating backyard veggies or digging with glove-free hands could be a potential new antidepressant therapy.

“What our research suggests is that eating, touching, and breathing a soil organism may be tied to the development of our immune system and our nervous system. But you have to understand that we fed our mice much more of that organism than you are likely to find in a peck of dirt — it was more like a drug dose.”

In fact, an entire raised bed in my garden is unlikely to contain as much M. vaccae as what Jenks was serving her mice.

Still wanting a treatment I could offer my patients, I called Jack Gilbert, a marine microbial ecologist by training, who teaches at the University of Chicago. Gilbert co-founded the Earth Microbiome Project and American Gut, two ambitious collaborative projects seeking to understand how humans and other animals interact with their microbial environments. Gilbert had previously shared with me that his son’s autism diagnosis had prompted his interest in the potential neuroregulatory effects of microbes.

When I asked him what I might advise my patients based on these findings, he sighed.

“Every talk I give, there are parents that want something. I totally get it. We want that thing that will help our kids feel better.

“All this research is really fascinating, but we don’t have enough information to make any claims. If I were to say to everyone, ‘Move to a farm, buy a dog, and eat more raw veggies,’ those statements would be vacuous from an experimental or clinical perspective.”

Speaking with Jenks and Gilbert reminded me that M. vaccae is not an isolated therapy. In fact, it is just one of an enormous palette of microbes that have been interacting and coevolving with us since our earliest days. Our immunological and psychological well-being likely depends on more early and frequent exposure to a diverse group of bacteria, fungi, protozoa, and worms than it does on any one organism.

These creatures, which interact with us through our skin, lungs, and gut, are what Graham Rook, physician, microbiologist, and professor emeritus at University College London, refers to as “Old Friends.” I met Rook last year at an evolutionary medicine meeting at the University of Arizona where he presented a series of compelling studies in support of his “Old Friend” theory of immune dysregulation: that a mismatch between our DNA and our modern microbe-depleted environment is responsible for a recent increase in chronic health problems, including autoimmune diseases and depression.

Our immunological and psychological well-being likely depends on more early and frequent exposure to a diverse group of bacteria, fungi, protozoa, and worms than it does on any one organism.

So what to advise my patients? I agree with Jenks and Gilbert. Microbiome research is still in its infancy, and there is much to discover before we can make definitive prescriptions. But there is compelling evidence that we need a diversity of organisms found in animals, plants, soil, water, and air for optimal functioning of our immune and nervous systems. I now equate preserving ecological diversity in our surroundings with protecting our own health.

On a large scale, we can begin to do this by increasing the diversity of what we grow on our farms because agriculture, covering more than a third of the earth’s land surface, is an obvious reservoir for biodiversity. Our prevailing system of crop monoculture has severely limited the variety of organisms hiding beneath the soil, lying on the plants, and roaming the fields. The herbicides and pesticides used in monocultures narrow this spectrum further. We can start to shift to a more diversified system of farming by patronizing farms that grow a range of crops and by educating friends, neighbors, medical providers, and lawmakers about the health importance of this type of agriculture.

Even closer to home, perhaps the best place for us each to begin is with our own backyard plot or window box. Planting a rainbow of seeds, avoiding the use of garden chemicals, nourishing the soil with plant matter, digging with our hands, and eating the bounty—while not guaranteed to replace a pharmaceutical grade antidepressant — is a wonderful chance to hang out with “Old Friends.”

Daphne Miller is a practicing family physician, associate professor at the University of California, San Francisco, senior adviser at the Prevention
Institute, and author of Farmacology and The Jungle Effect

It's OK If Winter Makes You Sad
Four scientific strategies for an emotionally authentic holiday season

Jason Marsh

Whoever wrote “The Most Wonderful Time of the Year” never had to endure a night of Hanukkah listening to their right-wing cousin rail against communism. Or had to make dinner for two dozen family members, who each has his own unique set of food (and family) intolerances. Or had to spend an entire Christmas alone while cheers and laughter erupted from the apartment down the hall.

Jason Marsh is the director of programs at UC Berkeley’s Greater Good Science Center and the founding editor in chief of Greater Good, the center’s online magazine. He is also a co-editor of two anthologies of Greater Good articles: The Compassionate Instinct (WW Norton) and Are We Born Racist? (Beacon Press). He has written for The Wall Street Journal, San Francisco Chronicle, the opinion section of CNN.com, and many other publications.

No doubt the holidays can foster joy and goodwill. But we all know they also can usher in a season of sadness, stress, and disappointment. Extended time with family can stir up painful memories and difficult emotions, and it can be hard for us to know how to handle those feelings. Watching our friends flaunt their seemingly blissful holidays on Facebook can make us feel worse.

Fortunately, psychological research suggests some effective strategies for the holiday blues — and flags some especially unhelpful ones. The upshot is that sadness and other tough emotions are not afflictions that we should try to avoid or overcome. Instead, if properly understood, they can help contribute to a healthy—and happy—life.

Here are four strategies to help you craft your own happiness recipe this holiday season (and the rest of your year).

1. Don't Force Cheer

At family gatherings with cousins you secretly can’t stand and in-laws who dole out backhanded compliments, it can be tempting to put on a happy face while you seethe inside. Indeed, that might even seem like the most mature response—no drama, no conflict.

But a 2011 study by researchers at Michigan State University and West Point might make you think twice. They followed dozens of bus drivers for two weeks, looking to see when they flashed fake versus genuine smiles at their passengers. (Bus drivers do a lot of smiling, it turns out.) The results show that on days when the drivers tried to put on an act and fake a good mood, their actual moods got worse. This was especially true for women.

Similarly, a 2012 study led by Maya Tamir of the Hebrew University of Jerusalem found that people who wanted to feel happy even when a situation called for a different emotional response, like anger, actually reported less happiness overall. And research by Iris Mauss of UC Berkeley suggests that people who really want to be happy actually derive less happiness from positive experiences, apparently because their expectations are too high. Again and again, trying to force happiness seems to backfire.

2. Don’t Suppress Sadness

The results of the bus driver study can be explained by researchers Oliver John of UC Berkeley and James Gross of Stanford, who found that “negative” feelings like sadness or anger only intensify when we try to suppress them. That’s because we feel bad about ourselves when our outward appearance contradicts how we truly feel inside. We don’t like to be inauthentic.

What’s more, when we suppress emotions like sadness, we deny them the important function they can serve in our lives. Sadness can signal that something is distressing us; if we don’t recognize that feeling, we might not take the necessary steps to improve our situation.

Expressing our sadness can also elicit comfort and compassion from those who care about us, strengthening our bonds. By contrast, suppressing our emotions can actually undermine our relationships: A study led by Sanjay Srivastava of the University of Oregon found that college students who bottled up their emotions experienced less social support, felt less close to others, and were less satisfied with their social lives.

3. Respond mindfully

But none of this is to endorse drowning in melancholy or lashing out at our in-laws. Some ways of processing and acting on our emotions are healthier than others.

Recently, scientists have been paying special attention to the benefits of mindfulness, the moment-by-moment awareness of our thoughts, feelings, and surroundings. A mindful response to an emotional trigger (e.g., overcooking the holiday turkey) means that you pause rather than react. Instead of berating yourself, you simply notice what you’re feeling without judging that response as right or wrong.

Studies suggest that a mindful response to a negative event reduces the amount of sadness we experience after that event, is associated with less depression and anxiety, and may even carry physiological benefits, like lowering our heart rates. It’s a way to avoid suppressing your emotions without reacting hastily or getting consumed by rumination. And, fortunately, mindfulness isn’t something you’re simply born with or without; research suggests it’s a skill you can cultivate over time.

4. Enjoy your emotional cocktail

Inevitably, the holidays will bring a mix of highs and lows. Perhaps the most important lesson to keep in mind is that this variety of emotions might be the best thing possible for your overall well-being.

That was the key insight from a study published last year by a team of researchers from Yale, Harvard Business School, and other institutions spanning four countries. Their survey of more than 37,000 people found that those who experienced more “emodiversity”—a greater variety and abundance of emotions—were less likely to be depressed than people who reported high levels of positive emotion. In fact, people with more emodiversity used less medication, visited the doctor less frequently, spent fewer days in the hospital, practiced better dietary and exercise habits, and smoked less.

In other words, sadness, anger, and other difficult emotions are like so many other staples of the holidays, from egg nog to office parties: In moderation, they’re nothing to fear. Just make sure you’re balancing them with other, lighter experiences. And don’t forget to give yourself a break.

Jason Marsh is the director of programs at UC Berkeley’s Greater Good Science Center and the founding editor in chief of Greater Good, the center’s online magazine. He is also a co-editor of two anthologies of Greater Good articles: The Compassionate Instinc (WW Norton) and Are We Born Racist? (Beacon Press). He has written for The Wall Street Journal, San Francisco Chronicle, the opinion section of CNN.com, and many other publications.